Adsorption method and apparatus for treating polluted gas streams

ABSTRACT

Gas-solid contact method and apparatus, especially apparatus for the adsorption of sulfur oxides from flue gas on a downwardly moving bed of granular carbon-containing adsorbent, said apparatus being provided with an adsorbent containing vessel having opposed perforate vertical walls for gas flow, each of said walls comprising A. A VERTICAL ROW OF LOUVERS DISPOSED IN A JALOUSIE-TYPE RELATIONSHIP, EACH OF SAID LOUVERS BEING INCLINED UPWARDLY, AND OUTWARDLY FROM THE AXIS OF THE VESSEL, SAID LOUVERS BEING SUBSTANTIALLY PARALLEL TO ONE ANOTHER, AND B. A VERTICAL ROW OF BAFFLES ARRANGED AT THE INNER SIDE OF SAID WALL ADJACENT TO AND BEHIND SAID LOUVERS, SAID BAFFLES BEING SUBSTANTIALLY PARALLEL TO SAID LOUVERS.

United States Patent [191 Johswich et al. 1 Jan. 9, 1973 54] ABSORPTIONMETHOD AND 3,405,508 10/1968 vPetersetal ..55 73 APPARATUS FOR TREATING1,787,878 1/1931 Warden-Stevens. ....34/l74 1,895,60l 1/1933 Beuthner....55/390 POLLUTED GAS STREAMS 2,635,575 4/1953 Watson ..55/79 [75]Inventors: Friedrich Johswich, Essen-Sud;

Werner Schindelbeck, Lovenich, Primary Examiner-Charles N. Hart both ofGermany Attorney-Millen, Raptes & White [73] Assignee: Chemiebau Dr. A.Zieren GmbH & i

' Co. KG, Koln-Braunsfeld, Germany [57] ABSTRACT v Gas-solid contactmethod and apparatus, especially [22] Flled' Sept 1970 apparatus for theadsorption of sulfur oxides from flue [21] Appl. No.: 71,511 gas on adownwardly moving bed of granular carboncontaining adsorbent, saidapparatus being provided with an adsorbent containing vessel havingopposed [30] Forelgn Applicatlon Pnomy Dam perforate vertical walls forgas flow, each of said walls Sept. 13, 1969 Germany ..1 19 46 457.4comprising I a. a vertical row of louvers disposed in a jalousie- 52 us.c1 ..ss/13, 55/390 type relationship, each of Said louvers being 511 1m.(:1. ..B01d 53/06 inclined upwardly, and utwardly from the axis of [58]w of Search "55/34 73 77 79 the vessel, said louvers being substantiallyparallel I 8 3 1 74 to one another, and 23/284 2 8 4/17 1 b. a verticalrow of baffles arranged at the inner side [56] References Cited of saidwall adjacent to and behind said louvers,

UNITED STATES PATENTS 9/1958 Grahek ..34/l74 said baffles beingsubstantially parallel to said louvers.

I 10 Claims, 2 Drawing Figures PATENTEUJAN 9 I975 N Mi INVENTORFRIEDRICH JOHSWICU WERNER SCHINDELBECK K 9 win,

ATTORNEYS ABSORPTION METHOD AND APPARATUS FOR TREATING POLLUTED GASSTREAMS BACKGROUND OF THE INVENTION This invention relates tomoving-bed, gas-solid contact method and apparatus, and in particular tosuch apparatus especially suitable for the adsorption of sulfur oxidesand/or nitrogen oxides from industrial waste gases, especially flue gas,on carbon-containing adsorl mixtures. For the adsorptive purification ofvery large l quantities of gas, however, for example in the adsorptionof sulfur oxides or nitrogen oxides, from flue gas or other waste gases,it is better to conduct the adsorbent continuously through theadsorption and desorption zones. Apparatus for conducting a continuousoperation can consist ofv at least one adsorber comprising a gravityflow vessel through which a moving bedof the adsorbent travels from topto bottom. The mutually opposite vertical walls of the vessel aregas-permeable and spaced a short distance from each other, as comparedto the length and height of the vessel, thereby enabling the adsorbentto flow downwardly at a substantially uniform rate in directionperpendicular to the flow of the gas. Such apparatus is disclosed inGerman Patent Application B 6570, Class l2e, 3/02.

In the adsorber described in said application, th walls serving for thepassage of gas are provided with holes longitudinally slotted at rightangles to the direction of the flow of adsorbent, the boundary lines ofthese holes lying in a plane inclined obliquely with respect to thewall. Such a perforated metal sheet is usually made of the so-calledexpanded metal. However, it was found that such expanded-metal walls aregradually clogged, especially when dust-containing gases are treated.Accordingly, the adsorbers must be cleaned periodically. This is notonly a relatively expensive and laborious procedure, but italso involvesdowntime of the adsorber as well as potential disruptions in theprocess. I

' SUMMARY OF THE INVENTION With a view towards improving adsorbers ofthe prior art, especially towards mitigating the problem associated withthe adsorber describedin the Gennan application, it isan object of thisinvention to provide a novel adsorption vessel.

In particular, it is an object to provide adsorption method andapparatus having at least one vertically disposed container for theadsorbent with transverse perforate entrance and exit sides for gasflow. The apparatus is to operate with dust-containing gases and/or withabrasive adsorbents, with little or no clogging of the wallperforations. Furthermore, the apparatus is to permit, in its preferredform, a substantially uniform downward flow of the adsorbent over theentire cross section of the adsorbent container, resulting in asubstantially uniform residence time and load for the adsorbent.

Upon further study of the specification and appended claims, otherobjects and advantages of the present invention will become apparent.

To attain these objects, the perforated vessel wall comprises a row oflouvers downwardly inclined from the outside toward the inside insubstantially parallel relationship, and arranged in the manner of ajalousie one above the other. Spaced behind, and adjacent to theselouvers, there is provided a second row of baffles. To appreciate thefunction of this combination of louvers and baffles, the operation ofthe of the adsorber is first explained, assuming that the baffles areabsent.

The finely divided adsorbent flowing downwardly in the vessel similarlyto a liquid, exerts a lateral pressure, forcing the adsorbent into thespaces between the louvers. Since the static pressure resulting from theflow in the interior of the vessel is considerably higher than the backpressure resulting from the weight of the minor amount of adsorbent,disposed in between the louvers, said minor amount of adsorbent remainssubstantially stationary and does not flow through the vessel with themain body of adsorbent. This means that incoming gas containing soliddust-like entrainment would meet a stationary layer of adsorbent betweenthe louvers and deposit the solid entrained material, therebyresultingin the stationary layer being rapidly clogged.

By providing the baffles, the flow of the adsorbent is changed markedly.In effect, the baffles absorb the static lateral pressure of thedownwardly flowing adsorbent and protect that minor portion of theadsorbent between the louvers from being exposed to the lateralpressure, thereby permitting that minor portion to combine with the mainflow of the adsorbent. The cooperation between louvers and pressurerelief baffles thus ensures a continuous flow of adsorbent in the zoneof the louvers, thereby removing a stationaryadsorbent phase betweenadjacent louvers. Thus, the dust taken up by the outermost layer ofadsorbent is entrained continuously into the main stream, together withthe adsorbent, so that clogging of the interspaces between the granulesof this layer due to the deposition of dust is well nigh impossible. I r

In accordance with the preferred embodiment of the invention, a pressurerelief baffle is associated with each louver. The baffle is generallynarrower than the louver by about 40 to 80, preferably 50 to percent,and is arranged, with respect to the louver, in such a manner that theside pressure on the lower zone of the volume of adsorbent disposedbetweentwo adjacent guidebaffles iscompletely orsubstantially'completely absorbed. The layer of adsorbent in thepressure-relieved space between the louver and relief baffle is thenfree to fall, aided by the flow of gas through the adsorber.

Preferably, the baffles are disposed substantially parallel with respectto the louvers. The space between the baffle and louver then is notsubjected to any constriction in the direction of flow, which wouldother- A wise impede the discharge of the dust-laden adsorbent.

On the other had, the baffles must extend only a limited distance intothe main flow of the adsorbent so as not to deleteriously impair thisflow. For example, where the space between the perforate vertical wallsis 0.85 meters, the distance between the louvers and associated bafflesis about 6 to 9, preferably 7.5 to 8.5 centimeters.

The louvers themselves are also disposed substantially parallel withrespect to one another. The overlapping of the louvers is arranged sothat the adsorbent slopingly passing under the bottom edge of a louverdoes not flow over the upper edge of the next-lower louver.

Advantageously, the upper edge of each baffle is disposed verticallyunderneath the bottom edge of the next-higher louver. In this manner, itis ensured that the adsorbentflowing downwardly between the louver andthe pressure relief baffle is deflectedat least partially by thenext-lower baffle toward the mainstream, thereby preventing an excessivedust accumulation in the sidestream between the louver and baffle.

Suitably, the inclination a of the guide'baffles with respect to theaxis of the container is smaller than the sloping angle [3 of theadsorbent. By sloping angle B is meant the angle of repose at whichsolids can be stored without a landslide.

The angle a can be changedby providing adjustable hinged setsof louversand baffles, depending on the nature of the adsorbent and other processfactors. Generally, however, this angle a is set at about 25 to 35,preferably 27 to 32. Also, the distance between the bottom edge of onelouver and the top edge of the next lower louver is generally about 20to 60, preferably about 35 to 45 cm.

Under the above conditions, the space between the louvers and baffle isfully utilized for the flow of adsor bent.

In a further and preferred embodiment of the invention, the adsorbentvessel is provided with at least one means for decelerating the. mainflow of adsorbent. Such means is arranged approximately in the centerbetween the center of the opposed perforated vessel walls. Thisdecelerating means is preferably in the form of a guide-like obstructiongenerally convex to the downward flow of adsorbent. This guide preventsthe falling speed of the adsorbent in the middle of the main body ofadsorbent'from becoming higher than in the boundary zones near theperforated vessel walls, where the velocity is somewhat lower owing tothe obstructions. In this way, the'resid'ence time of the adsorbent inthe vessel is made more uniform, and the. overall capacity of theadsorbent is utilized more efficiently. Preferably, the guide element orelements in the center of the vessel are designed in the shape of agabled roof or assubstantiallyhorizontal tubes. Thereby, the peak of thefalling velocityin the center of the velocity profile is reduced withouta substantial increase in the flow resistance of the gas.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE DRAWINGSFIG. 1 illustrates an adsorber vessel 1, the'walls thereof beingdesigned according to this invention both on the entrance. upstream side2 and the exit downstream. side 3. These walls consist of verticalstruts 4 to which are attached a large number of louvers 5 in a bentbetween thetop inlet and the bottom outlet of the vessel, therebypermitting a uniform residence time for the adsorbent.

The flow of adsorbent atthe wall can be seen more l clearly from FIG. 2.The. gas to be treated enters, in accordance with the arrows 8, into thevessel between the louvers 5. During this process, the gas first flowsthrough a layer 9 of adsorbent wherein a substantial portion of the dustcontained in the gas is separated.

The dust-laden adsorbent continuously travels downwardly in a tortuouspath between the louvers 5 and the baffles 6, according to thearrow 10.In each instance, at point 11,- a portion of the dust-laden adsorbent istransferred from the wall stream 10 into the mainstream 12,.7, while,from the mainstream 7, a portion of the adsorbent passes over into thewall stream 10. Due to the continuous transverse movement of the layers9 of adsorbent and the exchange of adsorbent between the wall stream 10and the mainstream 7, the passage of gas is not impaired by anexcessivev deposition ofdust particles in the outermost layers of theadsorbent. Fora description of the auxiliary equipment that can be usedwith the illustrated adsorption ap paratus, reference is invited toU.SI-Pat. No. 3,284,158.

The invention is not limited to the illustrated embodiment, but extendsto all gas-solid contact devices benefitted by a non-stationary,non-cloggable movement of solids at the wall of the vessel containingthe solids, e.g. chemical reactors, coolers, dryers, heaters andadsorbers. 0f particular application, however, is the adsorptiontreatment of flue gas containing at least 1 15 ppm by weight of finelydivided solids.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for, those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to. adapt it to various usages andconditions.- v

In this connection, it is-to be noted that the baffles of the inventionare substantially to completely corextensive in length with the louvers;otherwise, the baffles would not be able to absorb the lateral pressureof the moving bed.

The process wherein a carbon-containing adsorbent is employed to treatflue gas is described in U.S. Pat. Nos. 2,992,065 and 2,992,895.

What is claimed is:

1. In gas-solid contact apparatus comprising a vertically disposed,vessel having a perforate transverse wall 'for the flow of gas, theimprovement wherein said wall comprises:

a. a vertical row of louvers, each of said louversbeing inclinedupwardly, and outwardly from the axis of the vessel, said louvers beingsubstantially parallel to one another and defining permanent openingstherebetween to permit gas to enter said vessel, and a vertical row ofbaffles arranged at the inner side of said wall adjacent to and behindsaid louvers, said baffles being substantially parallel to said louversand defining a tortuous path between the louvers and baffles foradsorbent material moving downwardly therethrough.

2. Apparatus according to claim 1, wherein the top edge of each baffleis disposed vertically underneath essentially permanently positionedduring operation of the apparatus, and having a set angle of inclinationwith respect to the axis of the vessel.

7. Apparatus as defined by claim 6 wherein said set angle of inclinationis 25-35.

8. In a process of purifying flue gas containing sulfur oxides, whichprocess comprises passing a downwardly moving bed of carbon-containingadsorbent through a vertically disposed vessel having a perforatetransverse wall, and'passing said flue gas through said perforatetransverse wall into said downwardly-moving bed of adsorbent, theimprovement which comprises passing a portion of said downwardly movingbed in a tortuous path defined by (a) parallel permanently open louversinclined upwardly and outwardly in said transverse wall, and (b) avertical row of baffles arranged at the inner side of said wall adjacentto and behind said louvers, said baffles being substantially parallel tosaid louvers.

9. A process as defined by claim 8 wherein said baffles are inclined atan angle of about 25-35 with respect to the axis of the vessel.

10. A process as defined by claim 9 wherein said baffles are inclined atan angle of about 27-3 2

2. Apparatus according to claim 1, wherein the top edge of each baffleis disposed vertically underneath the bottom edge of the next-higherlouver.
 3. Apparatus according to claim 1, said vessel comprising two ofsaid transverse walls, said walls being opposite to one another. 4.Apparatus according to claim 1, further comprising at least one guidemeans disposed approximately in the center between said opposedperforate vessel walls, said means being for decelerating fallingsolids.
 5. Adsorption apparatus according to claim 4, wherein the guideelement is in the shape of a gabled roof.
 6. Apparatus according toclaim 1, said baffles being essentially permanently positioned duringoperation of the apparatus, and having a set angle of inclination withrespect to the axis of the vessel.
 7. Apparatus as defined by claim 6wherein said set angle of inclination is 25* - 35*.
 8. In a process ofpurifying flue gas containing sulfur oxides, which process comprisespassing a downwardly moving bed of carbon-containing adsorbent through avertically disposed vesSel having a perforate transverse wall, andpassing said flue gas through said perforate transverse wall into saiddownwardly-moving bed of adsorbent, the improvement which comprisespassing a portion of said downwardly moving bed in a tortuous pathdefined by (a) parallel permanently open louvers inclined upwardly andoutwardly in said transverse wall, and (b) a vertical row of bafflesarranged at the inner side of said wall adjacent to and behind saidlouvers, said baffles being substantially parallel to said louvers.
 9. Aprocess as defined by claim 8 wherein said baffles are inclined at anangle of about 25* - 35* with respect to the axis of the vessel.
 10. Aprocess as defined by claim 9 wherein said baffles are inclined at anangle of about 27* - 32*